view tests/test-split.t @ 40326:fed697fa1734

sqlitestore: file storage backend using SQLite

This commit provides an extension which uses SQLite to store file
data (as opposed to revlogs).

As the inline documentation describes, there are still several
aspects to the extension that are incomplete. But it's a start.
The extension does support basic clone, checkout, and commit
workflows, which makes it suitable for simple use cases.

One notable missing feature is support for "bundlerepos." This is
probably responsible for the most test failures when the extension
is activated as part of the test suite.

All revision data is stored in SQLite. Data is stored as zstd
compressed chunks (default if zstd is available), zlib compressed
chunks (default if zstd is not available), or raw chunks (if
configured or if a compressed delta is not smaller than the raw
delta). This makes things very similar to revlogs.

Unlike revlogs, the extension doesn't yet enforce a limit on delta
chain length. This is an obvious limitation and should be addressed.
This is somewhat mitigated by the use of zstd, which is much faster
than zlib to decompress.

There is a dedicated table for storing deltas. Deltas are stored
by the SHA-1 hash of their uncompressed content. The "fileindex" table
has columns that reference the delta for each revision and the base
delta that delta should be applied against. A recursive SQL query
is used to resolve the delta chain along with the delta data.

By storing deltas by hash, we are able to de-duplicate delta storage!
With revlogs, the same deltas in different revlogs would result in
duplicate storage of that delta. In this scheme, inserting the
duplicate delta is a no-op and delta chains simply reference the
existing delta.

When initially implementing this extension, I did not have
content-indexed deltas and deltas could be duplicated across files
(just like revlogs). When I implemented content-indexed deltas, the
size of the SQLite database for a full clone of mozilla-unified
dropped:

before: 2,554,261,504 bytes
after:  2,488,754,176 bytes

Surprisingly, this is still larger than the bytes size of revlog
files:

revlog files: 2,104,861,230 bytes
du -b:        2,254,381,614

I would have expected storage to be smaller since we're not limiting
delta chain length and since we're using zstd instead of zlib. I
suspect the SQLite indexes and per-column overhead account for the
bulk of the differences. (Keep in mind that revlog uses a 64-byte
packed struct for revision index data and deltas are stored without
padding. Aside from the 12 unused bytes in the 32 byte node field,
revlogs are pretty efficient.) Another source of overhead is file
name storage. With revlogs, file names are stored in the filesystem.
But with SQLite, we need to store file names in the database. This is
roughly equivalent to the size of the fncache file, which for the
mozilla-unified repository is ~34MB.

Since the SQLite database isn't append-only and since delta chains
can reference any delta, this opens some interesting possibilities.
For example, we could store deltas in reverse, such that fulltexts
are stored for newer revisions and deltas are applied to reconstruct
older revisions. This is likely a more optimal storage strategy for
version control, as new data tends to be more frequently accessed
than old data. We would obviously need wire protocol support for
transferring revision data from newest to oldest. And we would
probably need some kind of mechanism for "re-encoding" stores. But
it should be doable.

This extension is very much experimental quality. There are a handful
of features that don't work. It probably isn't suitable for day-to-day
use. But it could be used in limited cases (e.g. read-only checkouts
like in CI). And it is also a good proving ground for alternate
storage backends. As we continue to define interfaces for all things
storage, it will be useful to have a viable alternate storage backend
to see how things shake out in practice.

test-storage.py passes on Python 2 and introduces no new test failures on
Python 3. Having the storage-level unit tests has proved to be insanely
useful when developing this extension. Those tests caught numerous bugs
during development and I'm convinced this style of testing is the way
forward for ensuring alternate storage backends work as intended. Of
course, test coverage isn't close to what it needs to be. But it is
a start. And what coverage we have gives me confidence that basic store
functionality is implemented properly.

Differential Revision: https://phab.mercurial-scm.org/D4928

#testcases obsstore-on obsstore-off

  $ cat > $TESTTMP/editor.py <<EOF
  > #!"$PYTHON"
  > import os
  > import sys
  > path = os.path.join(os.environ['TESTTMP'], 'messages')
  > messages = open(path).read().split('--\n')
  > prompt = open(sys.argv[1]).read()
  > sys.stdout.write(''.join('EDITOR: %s' % l for l in prompt.splitlines(True)))
  > sys.stdout.flush()
  > with open(sys.argv[1], 'w') as f:
  >    f.write(messages[0])
  > with open(path, 'w') as f:
  >    f.write('--\n'.join(messages[1:]))
  > EOF

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > drawdag=$TESTDIR/drawdag.py
  > split=
  > [ui]
  > interactive=1
  > color=no
  > paginate=never
  > [diff]
  > git=1
  > unified=0
  > [alias]
  > glog=log -G -T '{rev}:{node|short} {desc} {bookmarks}\n'
  > EOF

#if obsstore-on
  $ cat >> $HGRCPATH <<EOF
  > [experimental]
  > evolution=all
  > EOF
#endif

  $ hg init a
  $ cd a

Nothing to split

  $ hg split
  nothing to split
  [1]

  $ hg commit -m empty --config ui.allowemptycommit=1
  $ hg split
  abort: cannot split an empty revision
  [255]

  $ rm -rf .hg
  $ hg init

Cannot split working directory

  $ hg split -r 'wdir()'
  abort: cannot split working directory
  [255]

Generate some content.  The sed filter drop CR on Windows, which is dropped in
the a > b line.

  $ $TESTDIR/seq.py 1 5 | sed 's/\r$//' >> a
  $ hg ci -m a1 -A a -q
  $ hg bookmark -i r1
  $ sed 's/1/11/;s/3/33/;s/5/55/' a > b
  $ mv b a
  $ hg ci -m a2 -q
  $ hg bookmark -i r2

Cannot split a public changeset

  $ hg phase --public -r 'all()'
  $ hg split .
  abort: cannot split public changeset
  (see 'hg help phases' for details)
  [255]

  $ hg phase --draft -f -r 'all()'

Cannot split while working directory is dirty

  $ touch dirty
  $ hg add dirty
  $ hg split .
  abort: uncommitted changes
  [255]
  $ hg forget dirty
  $ rm dirty

Make a clean directory for future tests to build off of

  $ cp -R . ../clean

Split a head

  $ hg bookmark r3

  $ hg split 'all()'
  abort: cannot split multiple revisions
  [255]

  $ runsplit() {
  > cat > $TESTTMP/messages <<EOF
  > split 1
  > --
  > split 2
  > --
  > split 3
  > EOF
  > cat <<EOF | hg split "$@"
  > y
  > y
  > y
  > y
  > y
  > y
  > EOF
  > }

  $ HGEDITOR=false runsplit
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -5,1 +5,1 @@ 4
  -5
  +55
  record this change to 'a'? [Ynesfdaq?] y
  
  transaction abort!
  rollback completed
  abort: edit failed: false exited with status 1
  [255]
  $ hg status

  $ HGEDITOR="\"$PYTHON\" $TESTTMP/editor.py"
  $ runsplit
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -5,1 +5,1 @@ 4
  -5
  +55
  record this change to 'a'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 1df0d5c5a3ab. Write commit message for the first split changeset.
  EDITOR: a2
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: changed a
  created new head
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -3,1 +3,1 @@ 2
  -3
  +33
  record this change to 'a'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 1df0d5c5a3ab. So far it has been split into:
  EDITOR: HG: - e704349bd21b: split 1
  EDITOR: HG: Write commit message for the next split changeset.
  EDITOR: a2
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: changed a
  diff --git a/a b/a
  1 hunks, 1 lines changed
  examine changes to 'a'? [Ynesfdaq?] y
  
  @@ -1,1 +1,1 @@
  -1
  +11
  record this change to 'a'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 1df0d5c5a3ab. So far it has been split into:
  EDITOR: HG: - e704349bd21b: split 1
  EDITOR: HG: - a09ad58faae3: split 2
  EDITOR: HG: Write commit message for the next split changeset.
  EDITOR: a2
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: changed a
  saved backup bundle to $TESTTMP/a/.hg/strip-backup/1df0d5c5a3ab-8341b760-split.hg (obsstore-off !)

#if obsstore-off
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        3:00eebaf8d2e2
   * r3                        3:00eebaf8d2e2
  $ hg glog -p
  @  3:00eebaf8d2e2 split 3 r2 r3
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -1,1 +1,1 @@
  |  -1
  |  +11
  |
  o  2:a09ad58faae3 split 2
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -3,1 +3,1 @@
  |  -3
  |  +33
  |
  o  1:e704349bd21b split 1
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -5,1 +5,1 @@
  |  -5
  |  +55
  |
  o  0:a61bcde8c529 a1 r1
     diff --git a/a b/a
     new file mode 100644
     --- /dev/null
     +++ b/a
     @@ -0,0 +1,5 @@
     +1
     +2
     +3
     +4
     +5
  
#else
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        4:00eebaf8d2e2
   * r3                        4:00eebaf8d2e2
  $ hg glog
  @  4:00eebaf8d2e2 split 3 r2 r3
  |
  o  3:a09ad58faae3 split 2
  |
  o  2:e704349bd21b split 1
  |
  o  0:a61bcde8c529 a1 r1
  
#endif

Split a head while working parent is not that head

  $ cp -R $TESTTMP/clean $TESTTMP/b
  $ cd $TESTTMP/b

  $ hg up 0 -q
  $ hg bookmark r3

  $ runsplit tip >/dev/null

#if obsstore-off
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        3:00eebaf8d2e2
   * r3                        0:a61bcde8c529
  $ hg glog
  o  3:00eebaf8d2e2 split 3 r2
  |
  o  2:a09ad58faae3 split 2
  |
  o  1:e704349bd21b split 1
  |
  @  0:a61bcde8c529 a1 r1 r3
  
#else
  $ hg bookmark
     r1                        0:a61bcde8c529
     r2                        4:00eebaf8d2e2
   * r3                        0:a61bcde8c529
  $ hg glog
  o  4:00eebaf8d2e2 split 3 r2
  |
  o  3:a09ad58faae3 split 2
  |
  o  2:e704349bd21b split 1
  |
  @  0:a61bcde8c529 a1 r1 r3
  
#endif

Split a non-head

  $ cp -R $TESTTMP/clean $TESTTMP/c
  $ cd $TESTTMP/c
  $ echo d > d
  $ hg ci -m d1 -A d
  $ hg bookmark -i d1
  $ echo 2 >> d
  $ hg ci -m d2
  $ echo 3 >> d
  $ hg ci -m d3
  $ hg bookmark -i d3
  $ hg up '.^' -q
  $ hg bookmark d2
  $ cp -R . ../d

  $ runsplit -r 1 | grep rebasing
  rebasing 2:b5c5ea414030 "d1" (d1)
  rebasing 3:f4a0a8d004cc "d2" (d2)
  rebasing 4:777940761eba "d3" (d3)
#if obsstore-off
  $ hg bookmark
     d1                        4:c4b449ef030e
   * d2                        5:c9dd00ab36a3
     d3                        6:19f476bc865c
     r1                        0:a61bcde8c529
     r2                        3:00eebaf8d2e2
  $ hg glog -p
  o  6:19f476bc865c d3 d3
  |  diff --git a/d b/d
  |  --- a/d
  |  +++ b/d
  |  @@ -2,0 +3,1 @@
  |  +3
  |
  @  5:c9dd00ab36a3 d2 d2
  |  diff --git a/d b/d
  |  --- a/d
  |  +++ b/d
  |  @@ -1,0 +2,1 @@
  |  +2
  |
  o  4:c4b449ef030e d1 d1
  |  diff --git a/d b/d
  |  new file mode 100644
  |  --- /dev/null
  |  +++ b/d
  |  @@ -0,0 +1,1 @@
  |  +d
  |
  o  3:00eebaf8d2e2 split 3 r2
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -1,1 +1,1 @@
  |  -1
  |  +11
  |
  o  2:a09ad58faae3 split 2
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -3,1 +3,1 @@
  |  -3
  |  +33
  |
  o  1:e704349bd21b split 1
  |  diff --git a/a b/a
  |  --- a/a
  |  +++ b/a
  |  @@ -5,1 +5,1 @@
  |  -5
  |  +55
  |
  o  0:a61bcde8c529 a1 r1
     diff --git a/a b/a
     new file mode 100644
     --- /dev/null
     +++ b/a
     @@ -0,0 +1,5 @@
     +1
     +2
     +3
     +4
     +5
  
#else
  $ hg bookmark
     d1                        8:c4b449ef030e
   * d2                        9:c9dd00ab36a3
     d3                        10:19f476bc865c
     r1                        0:a61bcde8c529
     r2                        7:00eebaf8d2e2
  $ hg glog
  o  10:19f476bc865c d3 d3
  |
  @  9:c9dd00ab36a3 d2 d2
  |
  o  8:c4b449ef030e d1 d1
  |
  o  7:00eebaf8d2e2 split 3 r2
  |
  o  6:a09ad58faae3 split 2
  |
  o  5:e704349bd21b split 1
  |
  o  0:a61bcde8c529 a1 r1
  
#endif

Split a non-head without rebase

  $ cd $TESTTMP/d
#if obsstore-off
  $ runsplit -r 1 --no-rebase
  abort: cannot split changeset with children without rebase
  [255]
#else
  $ runsplit -r 1 --no-rebase >/dev/null
  3 new orphan changesets
  $ hg bookmark
     d1                        2:b5c5ea414030
   * d2                        3:f4a0a8d004cc
     d3                        4:777940761eba
     r1                        0:a61bcde8c529
     r2                        7:00eebaf8d2e2

  $ hg glog
  o  7:00eebaf8d2e2 split 3 r2
  |
  o  6:a09ad58faae3 split 2
  |
  o  5:e704349bd21b split 1
  |
  | *  4:777940761eba d3 d3
  | |
  | @  3:f4a0a8d004cc d2 d2
  | |
  | *  2:b5c5ea414030 d1 d1
  | |
  | x  1:1df0d5c5a3ab a2
  |/
  o  0:a61bcde8c529 a1 r1
  
#endif

Split a non-head with obsoleted descendants

#if obsstore-on
  $ hg init $TESTTMP/e
  $ cd $TESTTMP/e
  $ hg debugdrawdag <<'EOS'
  >   H I   J
  >   | |   |
  >   F G1 G2  # amend: G1 -> G2
  >   | |  /   # prune: F
  >   C D E
  >    \|/
  >     B
  >     |
  >     A
  > EOS
  2 new orphan changesets
  $ eval `hg tags -T '{tag}={node}\n'`
  $ rm .hg/localtags
  $ hg split $B --config experimental.evolution=createmarkers
  abort: split would leave orphaned changesets behind
  [255]
  $ cat > $TESTTMP/messages <<EOF
  > Split B
  > EOF
  $ cat <<EOF | hg split $B
  > y
  > y
  > EOF
  diff --git a/B b/B
  new file mode 100644
  examine changes to 'B'? [Ynesfdaq?] y
  
  @@ -0,0 +1,1 @@
  +B
  \ No newline at end of file
  record this change to 'B'? [Ynesfdaq?] y
  
  EDITOR: HG: Splitting 112478962961. Write commit message for the first split changeset.
  EDITOR: B
  EDITOR: 
  EDITOR: 
  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  EDITOR: HG: Leave message empty to abort commit.
  EDITOR: HG: --
  EDITOR: HG: user: test
  EDITOR: HG: branch 'default'
  EDITOR: HG: added B
  created new head
  rebasing 2:26805aba1e60 "C"
  rebasing 3:be0ef73c17ad "D"
  rebasing 4:49cb92066bfd "E"
  rebasing 7:97a6268cc7ef "G2"
  rebasing 10:e2f1e425c0db "J"
  $ hg glog -r 'sort(all(), topo)'
  o  16:556c085f8b52 J
  |
  o  15:8761f6c9123f G2
  |
  o  14:a7aeffe59b65 E
  |
  | o  13:e1e914ede9ab D
  |/
  | o  12:01947e9b98aa C
  |/
  o  11:0947baa74d47 Split B
  |
  | *  9:88ede1d5ee13 I
  | |
  | x  6:af8cbf225b7b G1
  | |
  | x  3:be0ef73c17ad D
  | |
  | | *  8:74863e5b5074 H
  | | |
  | | x  5:ee481a2a1e69 F
  | | |
  | | x  2:26805aba1e60 C
  | |/
  | x  1:112478962961 B
  |/
  o  0:426bada5c675 A
  
#endif

Preserve secret phase in split

  $ cp -R $TESTTMP/clean $TESTTMP/phases1
  $ cd $TESTTMP/phases1
  $ hg phase --secret -fr tip
  $ hg log -T '{short(node)} {phase}\n'
  1df0d5c5a3ab secret
  a61bcde8c529 draft
  $ runsplit tip >/dev/null
  $ hg log -T '{short(node)} {phase}\n'
  00eebaf8d2e2 secret
  a09ad58faae3 secret
  e704349bd21b secret
  a61bcde8c529 draft

Do not move things to secret even if phases.new-commit=secret

  $ cp -R $TESTTMP/clean $TESTTMP/phases2
  $ cd $TESTTMP/phases2
  $ cat >> .hg/hgrc <<EOF
  > [phases]
  > new-commit=secret
  > EOF
  $ hg log -T '{short(node)} {phase}\n'
  1df0d5c5a3ab draft
  a61bcde8c529 draft
  $ runsplit tip >/dev/null
  $ hg log -T '{short(node)} {phase}\n'
  00eebaf8d2e2 draft
  a09ad58faae3 draft
  e704349bd21b draft
  a61bcde8c529 draft